The invention relates to methods, materials, and apparatus useful for reducing ammonia discharge from industrial and municipal waste streams and for ammonia recovery. One aspect of the invention involves ammonia absorption using activated zinc hydroxide. Another aspect of the invention involves ammonia absorption using sorbent for ligand exchange adsorption with a metal bound to a cation exchange resin. A further aspect of the invention involves the regeneration and reuse of absorption media.
Another aspect of the invention involves the direct treatment of ammonia waste streams with zinc sulfate and sulfuric acid and concentrating to cause crystallization of an ammonium zinc sulfate hydrate. Another aspect of the invention involves ammonia absorption using sorbent for ligand exchange adsorption with a metal bound to a cation exchange resin and the subsequent regeneration using zinc sulfate and sulfuric acid to form the ammonium zinc sulfate hydrate crystals. In both aspects, the crystals may then be heated to release NH3 and regenerate the zinc sulfate and sulfuric acid.
Ammonia in aqueous solution is present as an equilibrium system defined by:
NH4+⇄NH3+H+
with an equilibrium constant of:       K    a    =                              [                      NH            3                    ]                ⁡                  [                      H            +                    ]                            [                  NH          4          +                ]              =          5.848      xc3x97              10                  -          10                    
at 20xc2x0 C. Where [NH3] represents the concentration of dissolved neutral ammonia. Techniques available for the removal of ammonia from aqueous streams can normally only recover either the ionic [NH4+] or gaseous form of ammonia [NH3]. For efficient removal, adjusting the pH of the aqueous stream to a pH less than 7 or more than 11, maximizes the concentration of either the ionic or gaseous form of ammonia respectively. In actual practice, to maximize the concentration of gaseous ammonia, the pH is typically adjusted to a value greater than 11 using lime or sodium hydroxide.
The gaseous form of ammonia can be removed from water by air stripping where it is contacted with large volumes of air. As the volatility of ammonia increases with temperature, the current state-of-the art of air stripping occurs at higher temperatures. Many configurations of contacting equipment have been used, including countercurrent and crosscurrent stripping towers, spray towers, diffused aeration, and stripping ponds with and without agitation. The ammonia has been recovered from the air by contacting the ammonia-laden air with sulfuric acid solution to form a solution of ammonium sulfate.
Steam stripping has also been used commercially, especially in the removal of ammonia from sour waters. As with air stripping, steam stripping typically involves adjusting the pH to levels greater than 11 using lime or sodium hydroxide. One process for treating petroleum sour waters uses steam stripping which with further downstream processing results in the recovery of ammonia in an anhydrous form, see Leonard et al., xe2x80x9cTreating acid and sour gas: Waste water treating processxe2x80x9d, Chemical Engineering Progress, October, (1984), pp. 57-60. Mackenzie and King, xe2x80x9cCombined solvent extraction and stripping for removal and isolation of ammonia from sour watersxe2x80x9d, Industrial Eng. and Chem. Research, 24, (1985), pp. 1192-1200, have examined the combined use of steam stripping and solvent extraction for the removal of ammonia from sour waters with reduced steam consumption.
Cation exchange and zeolites have been used to recover the ammonium form of ammonia from aqueous streams, see for example Berry et al. xe2x80x9cRemoval of Ammonia From Wastewaterxe2x80x9d, U.S. Pat. No. 4,695,387 (1987), and Wirth, xe2x80x9cRecovery of ammonia or amine from a cation exchange resinxe2x80x9d, U.S. Pat. No. 4,263,145 (1981). For these uses the pH is typically adjusted to lower than neutral levels. Temperature plays a much less significant role than in stripping. The cation exchange resins or zeolites are then regenerated by treatment with metal hydroxide solutions to give gaseous ammonia for which the resins and zeolites have no affinity.
References in the literature appear for the use of liquid membranes, hollow fibers, and reverse osmosis to remove ammonia from aqueous streams, although none of these techniques have apparently been commercialized.
Ligand exchange adsorption has been used to recover ammonia. In ligand exchange adsorption, an ion exchange resin is loaded with a complexing metal ion such as Cu2+, Zn2+, Ni2+, Ag+, etc. (Helifferich, F., Ligand Exchange, I and II, Jnl. of the Am. Chem. Soc., No.84, pp.3237-3245, 1962). The metal ion then acts as a solid sorbent for ligands such as ammonia. In theory, each metal ion may adsorb a number of ligands up to its coordination number, normally 4 to 6. In practice, not all of these sites will be occupied by an ammonia molecule.
When applied to ammonia, ligand exchangers will only form complexes with the uncharged form of the ammonia. Dawson, in U.S. Pat. No. 3,842,000 (1974) applied ligand exchange to the removal of ammonia from aqueous streams. Dawson used Cu2+ as the metal ion because of its high amine complex formation constant and Dowex(trademark) A-1 as the ion exchange resin. Ammonia was adsorbed after adjusting the pH of the solution to 9-12 to increase the availability of dissolved gaseous ammonia. Contacting the ligand exchange resin with a solution of sulfuric, nitric, phosphoric, or hydrochloric acid regenerated the ligand exchange resin. However, metal is stripped from the resin with each regeneration when a strong acid is used (see immediately below).
Dobbs et al. in xe2x80x9cAmmonia removal from wastewater by ligand exchangexe2x80x9d, Adsorption and Ion Exchange, AIChE Symposium Series, 71(152), (1975), pp. 157-163, examined the use of dilute hydrochloric acid and Jeffrey, M., Removal of ammonia from wastewater using ligand exchange, M. S. Thesis, Louisiana State University, (1977)(see Regeneration pp.72-79), examined the use of dilute sulfuric acid as a regenerate for a Cu2+ ligand exchange resin. Both dilute hydrochloric acid and dilute sulfuric acid were found to be ineffective as they leached the copper from the resin at unacceptably high levels. Both Jeffrey (1977) and Dobbs et al. (1975, 1976) attempted to use heat to remove the ammonia from the ligand exchange resin. Jeffrey""s use of warm water up to 45xc2x0 C. removed some ammonia, but failed to prove an effective regeneration agent. Dobbs et al. (1975, and in U.S. Pat. No. 3,948,842) used 30 psig (21,000 kg/m2) steam as a regeneration agent. Although successful in regenerating most of the ligand exchange resins activity, the process was energy intensive and produced peak ammonia concentrations in the condensed steam of only 800 ppm.
An object of the invention is to provide an ammonia recovery process that is more economical than current methods for removal of ammonia from fluid streams.
Another object of the invention is to provide an ammonia recovery process that uses fewer chemicals than current processes or chemicals compatible with the original process application. Typically this involves regeneration and recycle of the sorbent material(s).
Another object of the invention is to reduce ammonia concentration in the effluent stream to very low levels (i.e. less than or equal to 10 ppm) or to control the ammonia concentration to meet environmental regulations.
Broadly the invention discloses methods and apparatus for the removal of ammonia from fluids, particularly industrial and municipal waste streams. The waste streams may be gaseous or liquid streams.
I. First General Embodiment
A first embodiment of the invention includes a method for recovering ammonia from a fluid by the steps of: contacting the fluid with a sorbent of metal loaded media; separating the sorbent containing ammonia from the fluid; separating the ammonia from the sorbent by contacting the sorbent with a regenerant of a non-chelating weak acid, wherein an ammonium regenerant salt is formed. In further embodiments there may be additional steps including separating the ammonium from the ammonium regenerant salt to form ammonia and free regenerant. The additional steps may include separating the ammonia from the ammonium regenerant salt with a step selected from the group including: heating, applying a vacuum and a combination thereof. More preferably the separation of the ammonium from the regenerant salt is by the step of contacting with a strong acid to form regenerant and an ammonium strong acid salt; and separating the regenerant therefrom. Typically the method includes recycling the separated sorbent and/or recycling the separated regenerant. Typically the weak acid may be a weak organic acid. Preferably the weak acid has a pKa between about 3 and about 7. The method may be augmented by further treatment including contacting and reacting the separated ammonia with nitric acid to form ammonium nitrate; and heating the ammonium nitrate and reacting at a temperature and pressure under hydrothermal conditions to decompose the ammonium nitrate to substantially nitrogen gas and water.
A more specific description of the first embodiment includes a method for recovering ammonia from a fluid including the steps of contacting the fluid with a sorbent including a metal ion loaded media, in a manner adapted to sorb ammonia on the sorbent; separating the ammoniated sorbent and the fluid; separating the ammonia from the sorbent by contacting the ammoniated sorbent with a non-chelating weak acid to form an ammonium regenerant salt; separating the ammonia from the regenerant by one or more steps selected from the group including heating the ammonium/regenerant complex; applying a vacuum to the ammonia/regenerant complex; or contacting the ammonia/regenerant complex with a strong acid.
Sorbent types useful in the invention typically include acrylamides, aminophosphonates, aminodiacetates, carboxylates, chelators, phosphonates, diphosphonates, and sulfonates.
A second further embodiment of the invention includes apparatus for recovering ammonia from a fluid including: a container enclosing a metal loaded media, the metal loaded media able to reversibly sorb ammonia; one or more inlet valves at an inlet portion of the container for admitting fluid or regenerant to the container; one or more outlet valves for exiting treated fluid or reacted regenerant at an outlet portion of the container; and a source of regenerant that is a non-chelating weak acid, operatively connected to an inlet valve at the admitting portion of the container. A further embodiment of the apparatus typically includes an ammonia separator for receiving and separating ammonia from the regenerant, operatively connected to one of the outlet valves. A yet further embodiment includes a chemical reactor operatively connected to the ammonia separator, for reacting separated ammonia from the separator with a strong acid; and a regenerant separator, operatively connected to the reactor, for separating the regenerant from the strong acid. A yet further embodiment includes recycling apparatus for providing regenerant from the regenerant separator to the inlet valve. An additional embodiment includes apparatus for degrading the ammonia with a reactor for mixing and reacting nitric acid, operatively connected to the ammonia separator, for producing ammonium nitrate; and a hydrothermal reactor, operatively connected to the reactor, for degrading the ammonium nitrate to substantially gaseous nitrogen and water.
A yet further embodiment of the apparatus for recovering ammonia from a fluid includes means for enclosing a metal loaded media able to reversibly sorb ammonia; inlet means, at an inlet portion of the means for enclosing, for admitting fluid or regenerant; outlet means, at an outlet portion of the means for enclosing, for exiting treated fluid or reacted regenerant; and regenerant source means including a non-chelating weak acid, operatively connected to the inlet means. Additional embodiments can include means for separating ammonia from the regenerant, operatively connected to the outlet means.
Another embodiment for the apparatus includes reactor means for receiving ammonia from the means for separating ammonia and reacting with a strong acid and means for separating the regenerant from the strong acid. Typically the apparatus includes means for recycling the sorbent and/ or regenerant. Other embodiments typically include means for separating ammonia from the reacted regenerant operatively connected to the outlet means. Additional apparatus includes means for reacting nitric acid, operatively connected to the means for separating ammonia, to produce ammonium nitrate; and means for hydrothermally reacting the ammonium nitrate, operatively connected to the means for reacting nitric acid, wherein the ammonium nitrate is reacted to essentially nitrogen and water.
Another embodiment of the invention includes methods for preparing metal loaded media including the steps of contacting the sorbent/resin with a solution of a soluble metal salt. The metal may be loaded at any pH where it is soluble. Loading is typically accomplished by increasing the metal ion concentration to the extent sufficient for outcompeting an H+ ion at the sorbent/resin loading site.
A second embodiment of the invention includes methods and apparatus for recovery of ammonia from fluids based on a metal hydroxide sorbent. These methods typically include the steps of: contacting the fluid with a sorbent that is a solid metal hydroxide, so as to load ammonia on the sorbent; separating the sorbent loaded ammonia from the fluid; separating the ammonia from the sorbent by contacting the sorbent with a regenerant comprising a non-chelating weak acid, wherein an ammonium regenerant salt is formed, at conditions where metal hydroxide is not substantially removed. Typically there are two methods that may be used to assure that the metal hydroxide is not removed and is not available as a sorbent. First, the weak non-chelating acid is added at a rate that keeps the pH above the dissolution point of the metal hydroxide. Secondly, the weak non-chelating acid is added at a rate where the metal hydroxide is not dissolved out of the system because the ultimate overall pH of the system is still high enough to trap and reprecipitate the metal hydroxide. The second method would be an advantage in overcoming surface fouling problems. In further embodiments there may be additional steps including separating the ammonium from the ammonium regenerant salt. The additional steps may include separating the ammonium from the regenerant with a step selected from the group including: heating, applying a vacuum, and/or contacting the salt with a strong acid to form regenerant and an ammonium strong acid salt; and separating the regenerant therefrom. Typically the method includes recycling the separated sorbent and/or recycling the separated regenerant. In another embodiment the regenerant acid is typically a weak organic acid or a weak inorganic acid with a pKa between about 3 and about 7. The method may be augmented by further treatment including contacting and reacting the separated ammonia with nitric acid to form ammonium nitrate; and heating the ammonium nitrate and reacting at a temperature and pressure under hydrothermal conditions to decompose the ammonium nitrate to substantially nitrogen gas and water.
A yet further embodiment discloses methods for treating an air stream containing ammonia including contacting the air stream with a slurry made up of particles of activated metal hydroxide, the particles dispersed in a liquid; or particles of metal loaded media, the particles dispersed in a liquid; and regenerating the particles and recovering the ammonia. The particles are typically separated from the fluid stream before prior to regenerating the particles. The particles having spent regenerant thereon may typically be regenerated with heat, a vacuum, with a weak acid, or a combination thereof. When activated metal hydroxide is selected, the additional step of regenerating the media with a weak acid must be made while maintaining the pH level above that where metal is stripped from the metal hydroxide particle.
Generally this is accomplished by slow addition of weak acid and while maintaining the overall pH above 6 and most preferably above 7.
II. Second General Embodiment
A first embodiment of the invention includes a method for recovering ammonia from a fluid by the steps of contacting the fluid with a sorbent of metal-loaded media, separating the ammonia-containing sorbent from the fluid, separating the ammonia from the sorbent by contacting the sorbent with a stripping solution of a strong acid and a metal salt, wherein an ammonium salt is formed with the metal salt in a spent regeneration solution, separating the spent regeneration solution and treating it to crystallize an ammonium-metal double salt therefrom. Typically, the crystallization is accomplished by increasing the concentration of the ammonium salt and metal salt in the spent regeneration solution by evaporation or by decreasing the temperature of highly concentrated solutions. If desired crystallization may be controlled by seeding.
Preferably the metal cation loaded on the metal-loaded media is derived from Ag, Al, Ca, Ce, Cd, Co, Cr, Cu, Fe (II and III), Hg, Mg, Mn, Ni, Pd, Zn, Zr. The metal cations may be used alone or in combination with one or more other metal cations. Preferably, the cation in the metal salt of the stripping solution derives from Ag, Al, Ca, Ce, Cd, Co, Cr, Cu, Fe (II and III), Hg, Mg, Mn, Ni, Pd, Zn, Zr. The metal cations may be used alone or in combination with one or more other metal cations. Preferably, at least some of the metal cations loaded on the metal-loaded media and the metal cations in the metal salt of the stripping solution are the same. More preferably, they are all the same. Zinc is preferred because of its nontoxic character in relation to animals and humans and its solubility properties as a salt and double salt.
Preferably, the strong acid in the stripping solution is sulfuric, sulfurous, phosphoric and/or hydrochloric. More preferably, the strong acid is sulfuric. Typically, the anion in the metal salt used in the stripping solution matches the anion of the strong acid.
Preferably, concentration of the ammonium salt and metal salt in the spent regeneration solution is increased above the solubility limit of the ammonium-metal double salt with a step selected from the group including: heating, applying a vacuum and a combination thereof. More preferably, these conditions will include seeding with recycled ammonium sulfate crystals to minimize scaling and to control crystallization rate and crystal size.
In further embodiments there may be additional steps including separating the ammonia from the double salt and recycling the stripping solution. The additional steps may include separating the ammonia from the ammonium-metal double salt by decomposition with heat.
Sorbent types useful in the invention typically include polymers of acrylamides containing metal complex groups of aminophosphonates, aminodiacetates, carboxylates, phosphonates, diphosphonates, and/or sulfonates including chelators made therefrom and mixtures of the foregoing.
A more preferred embodiment includes contacting an ammonia-laden wastewater stream with a zinc-loaded cation exchange resin to adsorb the ammonia, separating the zinc-loaded cation exchange resin containing the adsorbed ammonia and stripping the ammonia with a stripping solution of ZnSO4 and H2SO4 to form a spent regeneration solution of ammonium sulfate and zinc sulfate, and crystallizing zinc ammonium sulfate hydrate therefrom. The method preferably includes recovering the zinc ammonium sulfate hydrate and decomposing to recover ammonia. More preferably, zinc sulfate and sulfuric acid are recovered from the decomposition and recycled.
Crystallization of the zinc ammonium sulfate hydrate preferably includes evaporation of the spent regeneration solution in conventional manner by, for example, heating, vacuum or a combination of the two, and subsequent cooling. The amount of evaporation and cooling required depends upon the initial concentration of the ammonia. If the ammonia concentration is high enough (resulting in ammonium zinc sulfate hydrate concentration above the solubility limit) no evaporation may be required.
The crystals are preferably decomposed by heating wherein water and ammonia vapors are released. Typically, the decomposition includes heating at a lower temperature to remove water, and subsequently heating at a second higher temperature to remove ammonia. In certain situations, it may also be useful to drive the reaction further to release the SO2/SO3 and to then capture the gas as ammonium sulfate in conventional ways.
The ammonia may be captured as ammonia by condensation (particularly by multiple effect condensation) or as a salt by using an acid stripper. The acid stripper (for example, phosphoric or nitric) can be selected to enhance the market value of the ammonia. After crystallization of the spent regeneration solution, the remaining aqueous liquid may be further processed to recover ammonium sulfate or it may be recycled back directly for ammonia stripping.
A second embodiment of the invention includes methods and apparatus for direct reduction of ammonia from waste streams by reacting an aqueous ammonia stream with a stripping solution of a strong acid and a metal salt, wherein an ammonium salt is formed with the metal salt in a spent regeneration solution, separating the spent regeneration solution and treating it to crystallize an ammonium-metal double salt therefrom. Typically, the crystallization is accomplished by increasing the concentration of the ammonium salt and metal salt in the spent regeneration solution by evaporation or by decreasing the temperature of highly concentrated solutions.
Preferably, the cation in the metal salt of the stripping solution derives from Ag, Al, Ca, Ce, Cd, Co, Cr, Cu, Fe (II and III), Hg, Mg, Mn, Ni, Pd, Zn, Zr. The metal cations may be used alone or in combination with one or more other metal cations. Zinc is preferred because of its nontoxic character in relation to animals and humans and its solubility properties as a salt and double salt.
Preferably, the strong acid in the stripping solution is sulfuric, sulfurous, phosphoric and/or hydrochloric. More preferably, the strong acid is sulfuric. Typically, the anion in the metal salt used in the stripping solution is substantially the same anion as in the strong acid.
Preferably, concentration of the ammonium salt and metal salt in the spent regeneration solution is increased above the solubility limit of the ammonium-metal double salt with a step selected from the group including: heating, applying a vacuum and a combination thereof. Optionally, the process will include seeding with recycled ammonium sulfate crystals to minimize scaling and to control crystallization rate and crystal size.
In further embodiments there may be additional steps including separating the ammonia from the double salt and recycling the stripping solution substantially the same as described above for recovery of ammonia from the double salt in the first embodiment. The additional steps may include separating the ammonia from the ammonium-metal double salt by decomposition with heat.
A more preferred process for the direct reduction of ammonia from a waste stream includes reacting an aqueous ammonia stream with a zinc sulfate and sulfuric acid solution to produce a spent regeneration solution of zinc sulfate and ammonium sulfate and treating such solution to cause crystallization of zinc ammonium sulfate hydrate. Preferably, the crystallization is caused by concentrating the stream by removing water. Typically this is accomplished by evaporation by conventional heating, vacuum or a combination of the two. The crystallization may also be caused by reducing the temperature of the zinc sulfate/ammonium sulfate solution or by a combination of concentration and cooling.
The method may also include cooling the solution below the crystallization temperature and continuously or sequentially separating the crystals of zinc ammonium sulfate hydrate. Multiple crystallization steps may be used. Optionally, the method may also include recovering zinc from the liquid remaining from the crystallization step, preferably with a cation exchange resin or using liquidxe2x80x94liquid extraction, for example, and sulfuric acid regeneration, depending on the zinc concentration.
The method may also include the recovery of ammonia by decomposition of the zinc ammonium sulfate hydrate crystals to release NH3 and H2O, and may further include recovery of the remaining zinc sulfate and sulfuric acid, which are recycled. The decomposition step may preferably comprise heating the crystals at a lower temperature to remove water, and raising the temperature to a higher level to remove ammonia. Ammonia vapor may preferably be condensed to recover the ammonia or recovered as a salt by stripping with an acid.
The invention also includes apparatus for recovering ammonia from a fluid including: a fluid-contacting device containing an ammonia sorbent of metal-loaded media, means for contacting the ammonia-containing fluid with the ammonia sorbent and sorbing the ammonia thereon, means for removing the ammonia-depleted fluid from the contacting device, means for contacting the ammonia-loaded sorbent with a stripping solution of a strong acid and a metal salt to form a spent regeneration solution of ammonium salt and metal salt, and means for treating the spent regeneration solution to crystallize an ammonium-metal double salt therefrom. Typically, the apparatus also may include an evaporator for increasing the concentration of the ammonium salt and metal salt in the spent regeneration solution and/or a cooling device for cooling the spent regeneration to cause crystallization. The evaporator and the cooling device may be the same piece of apparatus.
The apparatus may also include one or more heating devices for decomposing the crystals to release the water and ammonia vapors. Typically, the apparatus also includes a condenser to recover the ammonia vapor or a contacting device to capture ammonia as a salt by using an acid stripper.
A yet further embodiment discloses methods for treating an air stream-containing ammonia including contacting the air stream directly with an aqueous stream of zinc sulfate and sulfuric acid or with particles of metal-loaded media which are thereafter stripped of ammonia by contact with a zinc sulfate/sulfuric acid solution; crystallizing ammonium zinc sulfate hydrate from the solution, and decomposing the latter to release the ammonia and regenerate the stripping solution.
The invention includes every novel feature and every novel combination of features disclosed in the specification herein.